Midwinter spring is its own season and the injector complex has started to shake off the relatively short but effective year-end technical stop (YETS).
On 14 February, H- ions were accelerated again to 160 MeV in Linac4 and taken in the direction of the Booster. Beam was taken into the Booster itself ahead of schedule on Friday, 18 February. Physics is slated to start at ISOLDE, n_TOF and the East Area on 28 March following the recommissioning of the Booster, the PS and the facilities. Progressive commissioning of the PS and SPS will see the restart of physics at the North Area and AD-ELENA’s experiments in the last week of April.
All sectors of the LHC are now cold, following the pre-Christmas warm-up and the subsequent successful replacement of the plug-in module with the buckled RF finger in sector 2-3 during the YETS. Some residual YETS activities are still ongoing in the tunnel, but the key was passed from the Coordination team to the LHC Operations team on 15 February. With electrical quality assurance (ELQA) completed in all sectors bar 2-3, the focus now shifts to the extensive powering test campaign of all magnet circuits, which is now under way, with around 8000 tests planned in all. Sector 2-3 should be ready to start its final dipole training to 6.8 TeV towards the end of March, when interleaved training and machine checkout will begin.
Commissioning of the LHC’s other accelerator systems, such as RF, collimation, beam instrumentation, beam dump and injection, transverse damper, vacuum and so on, is also under way. In parallel, all the LHC experiments will be continuing their final preparations, with some tight deadlines still to be met.
LHC beam commissioning with 450 GeV protons is scheduled to start on 11 April, with collisions at 450 GeV per beam expected around 10 May. Stable beams with collisions at 6.8 TeV per beam and nominal bunch population are scheduled for 15 June. This will be followed by a staged ramp-up in the number of bunches towards the year’s target of around 2700 bunches per beam. Following the long shutdown, electron cloud will be an issue and some sustained scrubbing is expected. Unidentified falling objects (UFOs) – now identified – might also hinder progress as we settle into Run 3.
It's been a long stop for the LHC and the experiments and there will be some excitement, and some relief, as we finally start Run 3 proper. The beam test of last October gave some indication that things are in good shape but there is still a way to go – the scale of the LHC enterprise should never be underestimated.
Looking further ahead, a revised long-term schedule for the LHC was approved by the CERN Council in December, based on recommendations from both the LHC Experiments Committee (LHCC) and the CERN Machine Advisory Committee (CMAC). Run 3 will now take us through until the end of 2025, with Long Shutdown 3 (LS3) lasting for three years instead of the previously envisaged two-and-a-half. The shift of LS3 will allow the teams to absorb the COVID-induced delays and effectively complete the construction work of the HL-LHC programme and the Phase 2 upgrades of the ATLAS and CMS experiments.
It's been a challenging two years and the progress on all fronts has been truly remarkable under the circumstances, laying the foundations for another good year in the injectors and the start of Run 3 in the LHC.